1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a wound core of a transformer.
2. Description of the Related Art
As the iron cores of transformers, wound cores in which a strip having excellent magnetic characteristics is wound in a ring shape are now used. For example, a wound core is obtained by winding a strip material on a winding spool to obtain a square, rectangular, stepwise, or circular cross-section. For this wound core, two split cylindrical coil bobbins are pressure welded at pressure welding faces thereof, and windings are wound on the coil bobbins. Also, a cut-core type is known in which a core is cut and separated at the leg portions thereof, and windings are inserted from the leg portions into the core, to complete a wound core.
When manufacturing the above-mentioned wound core, a strip having a predetermined shape is wound on a winding spool, and as a result, when the winding thickness of the winding spool reaches a predetermined thickness, this winding operation is stopped, and a wound core is obtained. In this case, if the winding thickness is too large, when pressure welded coil bobbins are applied to the wound core and rotated, the wound core scratches the inner surface of the coil bobbins, thereby seriously hindering the winding operation of windings. Also, sometimes it is impossible to perform the pressure welding operation because the coil bobbins have split into two pieces and cannot be joined together again. Conversely, if the winding thickness is too small, a large air gap is formed between the coil bobbins and the wound core, and thus the effective cross section is reduced, and accordingly, the amount of magnetic flux is reduced.
In prior art, the above-mentioned thickness is determined by a predetermined number of rotations of the winding spool. In this case, since the thickness of the strips is not always the same, this predetermined number may be larger than a desired value. Accordingly, when the winding spool has rotated a predetermined number of rotations, the thickness of a strip wound on the winding spool is actually measured, and it is then determined whether the winding operation should be continued or a part of the already wound strip removed. As a result, the efficiency of the winding of the wound cores is lowered and the loss of material is increased, thus increasing the cost of manufacturing the transformers (wound cores).
Similarly, when manufacturing a strip having a predetermined shape from a material having two straight edges, i.e., on both sides thereof, the material is cut by a slitter unit into a plurality of pieces of continuous strip for each core, this strip is wound on a temporary winding frame, and subsequently, the strip is wound on the winding spool, as explained above. In this case, since the width of the cut strip is not automatically controlled in accordance with the thickness of the strip, it is substantially impossible to obtain an absolutely precise predetermined cross section, such as a circular cross section, after the strip is wound on the winding spool. As a result, the effective cross section of the wound core is unsatisfactory, and therefore, the amount of magnetic flux is reduced, thus lowering the performance of the wound core.